Nutrient Excretion Rates of Anadromous Alewives during Their Spawning Migration

Abstract

Excretion is one of the processes through which anadromous fishes move marine-derived nutrients into freshwater ecosystems, but no direct estimates of nutrient excretion rates by anadromous fish exist. We estimated the mass-specific nutrient excretion rates of anadromous alewives Alosa pseudoharengus during their spring spawning migration into Bride Lake, Connecticut. Anadromous alewives excreted an average of 2.17 μg of phosphorus per gram of wet fish mass per hour and 24.71μg of nitrogen. The mean N:P ratio (by mass) of nutrient excretion was 11.7. Most of the nitrogen excreted was in the form of NH₄ ⁺. Our results suggest that excretion by anadromous fish can affect local food webs and ecosystem function when ecosystems are relatively small and fish aggregate at high densities, such as at the peak of the spawning run.